1. Field of the Invention
The present invention generally relates to a viewfinder assembly in a photographic camera and, more particularly, to the support of the viewfinder assembly, the connection of an eyepiece lens or a light measuring lens holder to the viewfinder assembly, and the protection of the viewfinder assembly.
2. Description of the Prior Art
As a substitute for a pentagonal roof prism forming the major component part of the photographic viewfinder of the single reflex camera, a viewfinding mirror module is currently utilized which comprises a plurality of reflecting mirrors so arranged and so positioned as to represent an appearance similar to the traditional prism. In general, the prior art viewfinding mirror module is of one-piece construction formed by the use of any known plastics molding technique, including a pair of major roof mirrors laid at a predetermined acute angle (90.degree.) relative to each other, side walls continued from respective lower edges of the roof mirrors to support such roof mirrors on a camera body, and an eyepiece support frame positioned rearwardly of the viewfinding mirror module. The viewfinding mirror module of the above described construction is fixedly mounted on a camera body either directly or through a viewfinder holder.
To mount the viewfinding mirror module on the camera body, various methods have hitherto been used. For example, according to the Japanese Utility Model Publication No. 47-24420, published Aug. 2, 1972, the use is made of tension spring members between the viewfinding mirror module and the camera body to retain the former resiliently in position on the camera body thereby to avoid any possible deformation of one or both of the major roof mirrors. According to the Japanese Utility Model Publication No. 47-33317, published Oct. 7, 1972, the viewfinding mirror module is fixedly mounted on the camera body by the use of set screws positioned beneath an eyepiece support frame and isolated in position from the major roof mirrors to avoid any possible build-up of stresses on the major roof mirrors.
According to the first mentioned method wherein the use has been made of the tension spring members, the tension spring members used has been found minimizing the effective utilization of a space exterior of and in the vicinity of the viewfinding mirror module. For example, if a flexible printed circuit board such as generally used in electronically controlled photographic cameras is mounted on and arranged exteriorly above the major roof mirrors, the presence of the tension spring members tends to constitute a cause of an increase in size of the camera body.
On the other hand, according to the second mentioned method wherein the set screws are used, the avoidance of the stress build-up on the major roof mirrors necessitates the screw member to be positioned at respective locations isolated from the major roof mirrors and, therefore, the eyepiece support area tends to protrude rearwardly away from the viewfinder mirror module with the freedom of layout limited consequently.
Although the use may be contemplated of a bonding agent to secure the viewfinding mirror module on the camera body, there may be a possibility that the bonding agent when cured undergoes a contraction to such an extent as to result in one or both of the major roof mirrors departing from a required geometric layout. A certain type of bonding agent such as containing, for example, silicone will hardly contract even when cured, however, it requires a long time to cure completely accompanied by a reduction in work efficiency. Considering the contraction and the curing time, the use of UV type bonding agent appears to be ideal, however, problematic in that relatively complicated facilities are required.
Also, as far as the retention of the eyepiece is concerned, it is a general practice to secure the eyepiece with the use of a bonding agent to the eyepiece support frame formed integrally with the major roof mirrors by the use of the plastics molding technique such as disclosed in, for example, the Japanese Utility Model Publication No. 47-33314, published Oct. 7, 1972. However, the use of the bonding agent to secure the eyepiece generally has a problem in that the preciseness with which the major roof mirrors are positioned tends to be adversely affected. Even though the silicone type bonding agent which is generally considered substantially free from contraction during a curing process is employed, the preciseness with which the major roof mirrors are positioned tends to be adversely affected due to the difference in coefficient of thermal expansion between the eyepiece and the viewfinding mirror module at relatively high or low temperature. As is well known to those skilled in the art, the lack of the positioning preciseness results in the presentation of a deformed or exaggerated image of the object or scene as it appears in the field of view of the lens.
When it comes to a light measuring lens or light measuring element generally positioned at a light exit surface of a pentagonal solid prism, the prior art is such that the light measuring lens or light measuring element is supported by a prism holder for the support of the pentagonal prism either directly or through an eyepiece holder.
When the above described technique generally practiced in the environment in which the solid prism is used is employed for securing the light measuring lens or light measuring element in the viewfinding mirror module, the following problems arise. Specifically, while in the viewfinding mirror module a light measuring opening in the vicinity of the light exit side where the eyepiece is fitted has to be sealed for dust-proof, a gap is necessary between the viewfinding mirror module and the light measuring lens or light measuring element where the latter is to be supported by the viewfinder holder and, therefore, the viewfinding mirror module cannot be completely sealed. Also, in order for the light measuring lens or light measuring element to be retained by the viewfinder holder, pillars stand on respective sides from the viewfinder holder while sandwiching the eyepiece, causing the viewfinding mirror module to become bulky.
Again, in the viewfinding mirror module, the major roof mirrors has to be precisely laid at an angle of 90.degree. relative to each other. If this precise angle is not attained, an image of the object or scene appearing in the field of view of the lens will be viewed as deformed or exaggerated. In particular, where members having a coefficient of thermal expansion different from that of the viewfinding mirror module are secured to the viewfinding mirror module, the positioning preciseness of the roof mirrors tends to be adversely affected at high or low temperature due to the difference in coefficient of thermal expansion.
In recent models of single lens reflex cameras having light-weight and compact features, the flexible printed circuit board having IC elements and other electric component parts mounted thereon is generally installed within a space delimited between the solid prism and a cover for protecting the solid prism because a relatively large space is available above the solid prism.
The installation of the flexible printed circuit board within a space between the viewfinding mirror module and the cover protecting the viewfinding mirror module is also disclosed in, for example, the Japanese Laid-open Utility Model Publication No. 53-494244, published in 1978.
However, since, unlike the viewfinder employing the solid prism, the viewfinding mirror module is formed by the use of the plastics molding technique, the viewfinding mirror module is susceptible to deformation when an external force is applied thereto. In particular, as hereinbefore discussed, the lack of the preciseness in positioning of the major roof mirrors results in the presentation of a deformed or exaggerated image of the object or scene as it appears in the field of view of the lens.
Accordingly, when the flexible printed circuit board is mounted direct on the viewfinding mirror module, and when the upper casing of the camera body is subsequently mounted thereover, the upper casing may press the major roof mirrors causing the latter to depart from the predetermined geometrical relationship with each other.